Dongli Zhang wrote:

On 2026-05-20 5:05 PM, Willem de Bruijn wrote:

quoted

Weiming Shi wrote:

quoted

tun_xdp_one() returns -EINVAL on a frame shorter than ETH_HLEN without
freeing the page that vhost_net_build_xdp() allocated for it.
tun_sendmsg() discards that -EINVAL and still returns total_len, so
vhost_tx_batch() takes the success path and never frees the page; each
short frame in a batch leaks one page-frag chunk.

A local process that can open /dev/net/tun and /dev/vhost-net can hit
this path: it attaches a tun/tap device as the vhost-net backend and
feeds TX descriptors whose length minus the virtio-net header is below
ETH_HLEN. Each kick leaks the page-frag chunks for that batch, and a
tight submission loop exhausts host memory and triggers an OOM panic.
Free the page before returning -EINVAL, matching the XDP-program error
path in the same function.

Fixes: 049584807f1d ("tun: add missing verification for short frame")
Reported-by: Xiang Mei <redacted>
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Weiming Shi <redacted>
---
 drivers/net/tun.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index b183189f1853..f594360d66d6 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2394,8 +2394,10 @@ static int tun_xdp_one(struct tun_struct *tun,
 	bool skb_xdp = false;
 	struct page *page;
 
-	if (unlikely(datasize < ETH_HLEN))
+	if (unlikely(datasize < ETH_HLEN)) {
+		put_page(virt_to_head_page(xdp->data));
 		return -EINVAL;
+	}

Make sense, thanks.

The error path from tun_xdp_act does the same. And the default: label
used to too, before a batching optimization was introduced.

Is the same then also missing if build_skb fails?

I also agree that we may need to handle build_skb() failure.

Thanks. Fine to defer to a separate patch btw. Either way.
 

In addition, I think we may need this fix for tap_get_user_xdp() as well.

Thank you very much!

Dongli Zhang